1. Field of the Invention
The present invention relates to an electrophotographic imaging apparatus such as a laser printer, and, more particularly, to an electrophotographic imaging apparatus including a pre-transfer erase assembly.
2. Description of the Related Art
An electrophotographic (EP) imaging apparatus such as a laser printer includes one or more transfer stations at which a different color toner is transferred to an image substrate. A mono-color laser printer typically includes a single transfer station, and a multi-color laser printer typically includes multiple transfer stations. In the case of a tri-color laser printer, it is known to provide four transfer stations, with each transfer station having a toner cartridge assembly carrying cyan, magenta, yellow or black toner.
It is also known to provide an image substrate in the form of an intermediate transfer member (ITM) such as an intermediate transfer belt to which the developed image is transferred. For example, the Lexmark Optra Color 1200 laser printers sold by the assignee of the present invention include four toner cartridge assemblies which are sequentially positioned along a substrate path defined by a media transport belt. Colored toner is sequentially developed onto selected dot locations of the latent image on each photoconductor drum that is associated with each cartridge thereby rendering visible a color latent image. Each transfer station causes a respective developed color toner image to transfer to and accumulate upon the transported medium. The composite developed and transferred color image is then fused using a fuser assembly.
It is known to provide a pre-transfer erase assembly within each transfer station prior to the latent image being transferred from the PC drum to the image substrate. For example, it is known to provide a transparent intermediate transfer belt and a Light Emitting Diode (LED) array positioned on a side of the ITM belt opposite from the PC drum. Light from the LED array shines through the ITM belt and partially discharges the PC drum. A pre-transfer erase assembly reduces the magnitude of electrostatic fringe fields holding toner onto the drum, thereby making more toner available for transfer to the print media. Moreover, the pre-transfer erase assembly reduces the voltage difference between the transfer roll/intervening media and the charge areas of the PC drum, thereby decreasing the likelihood of air ionization both pre-nip and post-nip. Reduction in the voltage differential reduces voiding and toner scatter which otherwise can result from air ionization.
A problem with a pre-transfer erase assembly as described above is that often times there is not sufficient space available within the printer to allow for use thereof. It is desirable to maintain the overall size of a printer as small as possible. With a multi-color printer, it is thus common to position four separate toner cartridge assemblies within tight geometric constraints. The limited space available heretofore has limited the use of pre-transfer erase assemblies.
What is needed in the art is a pre-transfer erase assembly for use in an electrophotographic printer which accommodates tight geometric constraints while at the same time providing sufficient illumination of the PC drum.
The present invention provides an electrophotographic image forming apparatus having a pre-transfer erase assembly which is carried by the frame of the image forming apparatus and positioned between a toner cartridge assembly and image substrate to illuminate a PC drum.
The invention comprises, in one form thereof, an electrophotographic image forming apparatus including a photoconductive drum and a transfer roll positioned adjacent to and defining a nip with the drum. An image substrate travels through the nip in an advance direction. A toner cartridge assembly is positioned in association with the drum and above the image substrate. A pre-transfer erase assembly having a light emitting outlet is positioned between the toner cartridge assembly and the image substrate. The light emitting outlet is directed toward the drum.
An advantage of the present invention is that the pre-transfer erase assembly may be used in conjunction with a transfer station having tight geometric constraints.
Another advantage is that the pre-transfer erase assembly is at least partially positioned in the space between the toner cartridge assembly and the image substrate.
Yet another advantage is that the light from the pre-transfer erase assembly may be selectively projected at different angles and varying areas of the PC drum.
A still further advantage is that different types of lights may be used with the light pipe and light guide.
Yet another advantage is that the light pipe and/or light guide may be formed as a hollow or solid body.
A further advantage is that when constructed as a solid body, the light pipe and/or light guide may include a fluorescent dye therein for receiving light at one wavelength and emitting light at a different wavelength.
Another advantage is that the light pipe and light guide may be mounted to and carried by the frame or toner cartridge assembly.